Interview: How to protect LED streetlight systems against input surges, and abnormal increase in input voltage

By BizLED Bureau

August 22, 2015: With the Indian government?s focus on energy efficiency, Littelfuse sees immense potential in LED streetlight market in India. A popular brand in the circuit protection vertical, it offers a wide range of circuit protection products, enabling comprehensive solutions for customers? unique needs.

In conversation with BizLED, Bharat Shenoy, Director of Technical Marketing, Electronics Business Unit, Littelfuse, explains how to protect LED streetlight systems against induced lightning surges and switching surges.

BizLED: Littelfuse has entered the Indian LED market. How do you see the potential of the Indian LED streetlight market?

Littelfuse: With the Indian government?s focus on energy efficiency, LED streetlight in India seems to have immense potential in the next few years.

BizLED: How does Littelfuse maintain its edge over India made products and China made products that have flooded the Indian market?

Littelfuse: Littelfuse is about 90-year-old circuit protection manufacturer, and we have a thorough understanding and experience about the circuit protection challenges and ways to resolve them, which helps us introduce innovative products and maintain our edge over other products in the market.

BizLED: India lacks any defined standards for LED streetlight protection. What kind of protection needs to be used?

Littelfuse: Robust and adequate protection needs to be used to ensure that luminaire investments can work under harsh outdoor conditions for longer lifetimes of 7-10 years, which is required by tendering agencies. This protection includes overcurrent devices such as fuses as well as lightning and other surge protection such as varistor-based products.

BizLED: How to protect LED streetlight system against input surges, and abnormal increase in input voltage, which India faces frequently?

Littelfuse: Both of these topics need to be dealt separately. Input surges are very high voltage, short duration events for which surge protection devices (SPD) need to be used while abnormal increase of voltages are comparatively lower voltage, longer time durations events for which LED drivers need to have separate protection built into them.

BizLED: How to protect LED streetlight system against induced lightning surges and switching surges?

Littelfuse: The basic protection element for both remains the same?SPD, but its needs to be understood that induced lighting surges can have voltages as high as 20kV and may happen only few times in a year, but switching surges can range from 4kV-10kV, but will be much more frequent and may happen even few times in a day. So SPD should be rated for high voltages like 20kV, but also de-rated (by using multiple hit 20kV/10kA SPD) for much frequent lower voltages surges to ensure longer lifetime of streetlight investments.

BizLED: Most LED streetlights in India are being designed for a protection of up to 6KV/3KA. Is this sufficient?

Littelfuse: 6kV/3kA does not seem to be sufficient for outdoor streetlights investments. LED lighting is a sensitive technology which is being used in a harsh environment where induced lightning surges can go up to 20kV/10kA and frequent switching surges can rapidly degrade a lower rated surge protection device. Worldwide standard bodies like ANSI have done extensive research on LED lighting surge protection, and have adopted 20kV/10kA multiple hit surge protection for outdoor luminaire to ensure their costly luminaire investments are well safeguarded.

BizLED: How metal oxide varistor (MOV) can protect against these surges? What are its limitations?

Littelfuse: MOV is a ceramic based voltage clamping device, which offers very high impedance during normal operating voltage. But when a surge voltage is applied to it, it clamps the voltage to a safer level and dissipates the excess surge energy across it, thereby protecting the circuit connected to it. As it is a ceramic device, it has a limited lifetime, which degrades over time through intended use.

BizLED: Please explain the advantages of UltraMOV from Littelfuse, and how is it better than the standard ones found in the Indian market?

Littelfuse: Littelfuse does continuous developments on its products. We have developed a new formula for MOVs with which we can achieve higher energy levels in smaller disc size, so we can offer the same performance of a standard 20mm MOV in new 14mm size.

BizLED: What happens when MOV starts degrading? What solution does Littelfuse offers against this problem?

Littelfuse: When MOV starts degrading, it will start to leak more current even at nominal operating voltages, so a time comes when the MOV will leak enough current during normal operating condition (when it should ideally not pass any current) and start to dissipate power and go into a thermal runaway and can catch fire. Littelfuse innovated thermally protected MOVs (TMOVs) where we used a special integrated thermal fuse to sense the MOV end of life and before the MOV goes into thermal runaway, it is disconnected from the circuit, thereby protecting the circuit from an immediate failure. We have also introduced a 3-lead TMOV where the third lead provides indication feature and user can give an alert to initiate a service call once the MOV reaches end of life.

BizLED: What solution do you have for protecting streetlight fixtures from adverse conditions?

Littelfuse: Littelfuse have a wide range of surge protection modules (SPDs), the LSP10-series, to offer for protecting streetlight fixtures from switching and lightning induced surges. Littelfuse introduced the world?s first series connected thermally protected SPD, where we innovatively place the thermal disconnect element in series with the output so that once the SPD reaches the end of life, the output is disconnected from the input. Now, as the light is turned off, the user gets an indication of service call to replace the SPD. The luminaire is also protected from subsequent surges before the replacement of SPD happens, thereby providing complete protection. Littelfuse SPD also offers self-protection against abnormal overvoltage and are available in multiple voltage options to suit all kind of customer requirements.

BizLED: In the Indian scenario, it is difficult to protect the streetlight system even with SPD module. Please share some tips for the designers.

Littelfuse: SPDs protect against most severe threat of transients to the streetlight system, but there are other events like neutral missing for which LED driver needs to have inbuilt protection while SPDs also need to be suitably rated. Earthing also plays very important role in protecting the sensitive LED luminaire from surges whereas the conventional lighting fixtures are comparatively robust and could work without earthing.

BizLED: What are the products Littelfuse offers for protecting LED streetlights?

Littelfuse: Littelfuse offers a wide range of circuit protection devices for LED streetlight like SPDs, MOVs, fuses, GDTs (gas discharge tubes), TVS diodes, resettable PPTCs and PLEDs. We also offer reed switch sensing solutions, which can be used for tamper detection, and ESD protection devices for any communication interfaces.